From the perspective of environmental protection and energy saving, a hybrid electric vehicle using an engine and a motor together as a power source has been developed and commercialized. Furthermore, in the future the development of a fuel cell hybrid electric vehicle, in which a fuel cell is used in place of an engine, will also become popular.
For example, Non-Patent Document 1 proposes a battery wherein vinylene carbonate is added to an electrolyte comprising LiPF6, ethylene carbonate and dimethyl carbonate in an amount of 2 wt. % whereby an increase in resistance (deterioration) can be suppressed for a period of high temperature (60° C.) storage.    [Non-Patent Document 1] Journal of The Electrochemical Society, 151(10) A1659-A1669 (2004).